The objective of this project is to study both the induction and effector step of cell-mediated cytotoxicity with the ultimate goal to find ways and means to manipulate this effector arm of the immune system. The specific aims of this project are: 1) to elucidate how immunoadjuvants like Vitamin A derivatives stimulate cell-mediated cytotoxicity and how this observation can be used in the suppression of tumor growth in animal model systems, 2) to find out whether Vitamin A derivatives have stimulating effects on the induction of cell-mediated cytotoxicity in an in vitro human model system, 3) to explore how the precursor cells of cytotoxic lymphocytes obtain their specificity for normal or modified histocompatibility antigens and whether the interaction of these lymphocytes with their targets requires receptors of one or several different specificities.